The present invention relates to antennas and more particularly to the single element VHF to UHF directional antenna.
Radio direction-finding antennas make use of the difference in the time of arrival of the wave front at different points of the receiving antenna system, whether it be a parabolic mirror focussing all parallel rays to a common point, or an array of discrete antenna elements. Hertz and Marconi used parabolic mirrors, and practical systems involving discrete elements were thoroughly understood and in use by the early part of the century.
Arrays of discrete elements are particularly suitable in the VHF and UHF range of signals, where loop systems are inefficient and parabolic reflectors would be too physically large for most applications. The following discussion is concerned principally with vertically-polarized waves in this portion of the spectrum.
A typical directional antenna comprises an array of quarter-wave elements mounted on a ground plane. Another type of directional antenna comprises four half wave dipoles vertically mounted on a mast. In this type of antenna, the signal arrives at the various elements at different times, so that the outputs are in varying phase relationship with each other and are used in a number of various ways to determine the bearing of an incoming signal. These systems are also useful in directional transmitting applications as well as for receiving.